The concept of using geosynthetic clay liners made with bentonite for lining landfill sites is well-known. The problem addressed by the present invention involves the prevention of the geosynthetic clay liner (GCL) from sliding down the slope or embankment surrounding the periphery of the landfill. The present invention may also be used in the construction of man-made lakes and ponds.
A GCL is commonly comprised of three major parts: (1) the primary carrier sheet, also known as the primary backing, primary textile or primary carrier; (2) a cover sheet, also known as the secondary textile, secondary carrier sheet or scrim; and (3) a layer of bentonite disposed therebetween.
Geosynthetic clay liners in current use are normally sewn or needle punched together to enhance the internal sheer strength of the liner and improve the performance of the liners when they are used on sloped surfaces. However, enhancing the internal sheer strength of the liners does not address the problem of the liners sliding down a slope or embankment during or after installation. If the liner is installed during wet conditions, this slippage problem is even more prevalent. Simply put, no geosynthetic clay liner found in the prior art provides an increased coefficient of friction between the underside of the liner and the surface in direct contact with the underside of the liner.
The inability of geosynthetic clay liners to maintain their position on steep slopes can also stem from the granular bentonite contained within the liner. Bentonite is a clay material that expands and becomes substantially impermeable upon being exposed to water. The layer of bentonite contained with the liners creates a low permeability barrier at the bottom of landfills. However, wet bentonite is extremely slippery. If any bentonite migrates through the lower sheet of the liner, the slippery bentonite will contribute to the inability of geosynthetic clay liner to maintain its positions on steep slopes and embankments. If the liner is made with tightly woven sheets or sheets with a closed structure that does not permit any leakage of bentonite, the sheets themselves may be slippery and contribute to the inability of the liner to maintain its position on a slope or embarkment.
Another problem associated with the use of geosynthetic clay liners on slopes or embankments is the downward sliding of cover soil after it is placed on top of the liner. Once installed, the liners are routinely covered with a layer of soil, i.e. cover soil. On steep slopes, the cover soil will often slide right off the upper surface of the liner. Therefore, a liner with a friction enhanced upper surface is needed to facilitate the placement of cover soil on top of the just-installed liner.
Many geosynthetic clay liners employing bentonite are restricted to slopes with a 4:1 ratio, that is, a horizontal to vertical ratio of 4:1. The development of liners with improved resistance to internal sheer stresses has improved this ratio to less than 4:1 and often obtaining ratios of less than 2:1. However, by providing a geosynthetic clay liner with a friction enhanced undersurface, it is expected that slope ratios will approach 1:1 when the internal sheer resistant techniques taught by the prior art are combined with the friction enhancement techniques taught by the present invention.
Thus, there is a need for an improved geosynthetic clay liner with an undersurface that provides enhanced frictional engagement between the undersurface of the liner and the slope or embankment that is in contact with the undersurface of the liner. There is also a need for an improved geosynthetic clay liner with an upper surface that provides enhanced frictional engagement between the upper surface of the liner and the cover soil.